This invention has relation to the use of a boring machine having a boring bar rotating on a horizontal axis to machine vertical, plane, discoid faces on work pieces where the center of the discoid face to be machined lies at the center of the axis of the boring bar rotation. The invention is particularly related to the problem of machining such a discoid face in a surface of a work piece which cannot be brought into face-to-face relationship with the boring machine and the boring bar extending outwardly therefrom.
In order to accomplish such back facing before the present invention, it was common to fasten an essentially J-shape attachment onto the boring bar, extending the vertical shank of the "J" through an opening in the work piece concentric with the discoid surface to be machined, with a tool bit positioned at the outside hook end of the "J". A slide extending radially outwardly from the axis of rotation of the boring bar was situated between the J-shape attachment and the boring bar. An attachment holder was positioned on the slide and was connected by appropriate gearing to a star wheel at the outer end of the slide. The parts were arranged in such a manner that the star wheel collided with an obstruction on every rotation of the boring bar; and with every such collision, the star wheel turned through an angle to move the attachment holder along the slide to cause the tool bit to be suddenly moved radially outwardly with respect to the boring bar axis.
This structure had a number of disadvantages. First, there was a springiness to the action of the tool bit in making its cut because it was at the end of a J-shape attachment, fastened to an attachment holder which was mounted in a slide which was mounted to the boring bar. Second, the method of feeding the tool bit forward was unsatisfactory because the tool bit moved forward once each revolution of the slide, the movement coming with a jerk each time the star wheels hit the obstruction. The net result was the production of a machined surface having substantially less than the accuracy desired.
Further, the size of the hole or opening in the work piece determined the radial dimension of the facing cut which could be made before the relationship of a J-shape attachment and the attachment holder on the slide had to be changed. As a result, the original set-up time and the changes in set up during the facing operation were considerable.
A patent which discloses a boring machine tool which has hydraulic apparatus for laterally displacing a rotating tool bit is U.S. Pat. No. 3,937,586 to Watson, granted in February of 1976. It does not disclose any means of performing a back facing operation.
A facing head in which a slide supporting a tool holder and a tool bit is shiftable radially at the front of a supporting body in order that face machining takes place at a work piece is disclosed in U.S. Pat. No. 4,067,252, granted to Eckle et al in January of 1978. Adjustment of the slide is obtained through movement of an adjusting rod located concentric with the axis of the spindle of the boring bar. Such a structure could not be adapted to do reverse facing, and no disclosure relative thereto is present in this patent.
U.S. Pat. No. 3,286,556 to Reynolds et al, granted in November of 1966 discloses a boring head with means for radially adjusting or moving a cutting tool on the head while the boring spindle is rotating. This structure could not possibly be adapted to back facing, and no such reference is made in this patent.
U.S. Pat. No. 3,422,705 to Nahodil et al, granted in January of 1969, also shows a boring head having means to drive a tool radially of the head. Like the aforementioned prior art patents, the support for the machine tool is such that the structure cannot be adapted for back facing. The Nahodil et al structure is useful as a recessing tool.
U.S. Pat. No. 3,599,517 granted to Muller in August of 1971 shows a boring head having a means to drive a tool radially of the head. Because of the structure of the boring head, it cannot be adapted to perform a back facing operation either.
A preliminary search was made on the structure of this invention, and the patents cited above were the closest patents located on this search.
The inventor and those in privity with him know of no prior art structures closer than those described in this application; and they acknowledge their responsibility to bring any more pertinent prior art to the attention of the Examiner should such prior art subsequently become known to them.
The structure of the present invention was designed to make possible efficient and accurate back facing of surfaces lying in a plane normal to the axis of a boring bar, and to overcome the inherent difficulties present in the prior art means of accomplishing this result.